The Liquid Crystal Display (LCD for short) has numerous advantages such as a thin body, power saving et al, and thus it is used widely. Most of the liquid crystal display devices on the market are backlight type liquid crystal display devices, of which each includes a liquid crystal panel and a backlight module. The operating principle of the liquid crystal panel goes as follows: liquid crystal molecules are placed between two pieces of parallel glass substrates; a number of vertical and horizontal fine wires are present between the two pieces of parallel glass substrates so as to control the liquid crystal molecules to change directions by means of powering on or off, thereby reflecting out the light that comes from the backlight module for generating pictures. Since the liquid crystal panel does not emit light itself, the liquid crystal panel displays images with help of a light source provided by the backlight module. Accordingly, the backlight module becomes one of the key components of the liquid crystal display device. According to different incident positions of a light source, the backlight module can be divided into two types, i.e. a side type backlight module and a direct type backlight module. As for the direct type backlight module, a light emitting source such as a cold cathode fluorescent lamp (CCFL for short) or a light emitting diode (LED for short) is disposed behind the liquid crystal panel and directly forms a surface light source for the liquid crystal panel. As for the side type backlight module, a LED light bar of the backlight source is disposed at an edge of the back plate behind the liquid crystal panel side, light emitted from the LED light bar enters a light guide plate from a light incidence surface of the light guide plate and is emitted out from a light emitting surface of the light guide plate after undergoing reflection and the diffusion, and finally forms a surface light source for the liquid crystal panel via an optical film set.
The direct type backlight sources are mostly used in the liquid crystal display products of large sizes such as a computer, a television and the like, and the side type backlight sources are mostly used in the liquid crystal display products of small sizes such as a tablet computer, a mobile phone and the like. In the backlight module of the side type backlight source in the relevant art, the light guide panel is positioned relative to the back plate by a recess defined in an edge of the light guide plate. In addition, regarding the design scheme in the related art, a gap of about 1 mm needs to be pre-reserved between the recess of the light guide plate and the back plate upon designing for ensuring that the light guide panel can have free space for expansion and contraction when performing a reliability test. The above-mentioned method of pre-reserving gap indeed ensures the expansion and contraction of the light guide plate. However, the light guide plate and the light bar are not easily to be aligned accurately upon assembling. As a result, the assembly of the light guide plate is shifted, which results in uneven brightness of the formed display screen and uneven light and dark phenomenon occurring at displayed pictures, thereby seriously affecting display quality of the pictures.